Computing 205/406 & IT8

Tutorial #13

1. In the lecture, the concept of ISDN "B Channel aggregation" was mentioned, and it was stated this was (until recently) considered a difficult problem.
   1. Why was this the case?
   2. The semi permanent Internet link between bendigo and Bundoora runs at 252 Kbps. Why such a funny number?

2. Two aspects of the ISDN service which are emphasised by the marketing people are "dial on demand" routing, and "bandwidth on demand" data transfer. What do you think these terms refer to? How do the ISDN call tariffs (see last tute) relate to these?

3. Rework the "Bendigo to Castlemaine" problem of question 3 of tutorial #12 for the case of a semi-permanent ISDN link (single B channel semi-permanent, 26-50 km, is $5940 p.a.)

4. Explain how a frame relay service at a port speed of 64 kbps differs from an ISDN semi permanent link at the same speed. In particular, why would you expect the frame relay service to be cheaper?

5. How is it possible for a frame relay service to drop frames? How can a user recover if this happens?

6. The ISDN service fits into a system called the "synchronous digital hierarchy" (SDH).
   1. What does this expression mean?
   2. What aspect of this system is said to be inefficient, and how does ATM overcome the inefficiency?